Electrode assemblies and associated fixation members for implantable medical devices

Abstract

A fixation member of an electrode assembly for an implantable medical device includes a tissue engaging portion extending along a circular path, between a piercing distal tip thereof and a fixed end of the member. The circular path extends around a longitudinal axis of the assembly. A helical structure of the assembly, which includes an electrode surface formed thereon and a piercing distal tip, also extends around the longitudinal axis and is located within a perimeter of the circular path. The tissue engaging portion of the fixation member extends from the distal tip thereof in a direction along the circular path that is the same as that in which the helical structure extends from the distal tip thereof. The electrode assembly may include a pair of the fixation members, wherein each tissue engaging portion may extend approximately one half turn along the circular path.

The invention claimed is: 
     
       1. An electrode assembly for an implantable medical device, the assembly comprising a longitudinal axis, a helical structure coupled to a distal portion of the device and extending distally from the distal portion and around the longitudinal axis, a first electrode surface formed on the helical structure, and a second electrode surface electrically isolated from the first electrode surface, the helical structure including a piercing distal tip located adjacent to the first electrode surface; and an improvement to the assembly comprising: a pair of fixation members, wherein each fixation member of the pair comprises:
 a fixed end coupled to the distal portion of the device; and 
 a tissue engaging portion terminated by a piercing distal tip, each tissue engaging portion extending from the corresponding distal tip to the corresponding fixed end along a circular path, the helical structure being located within a perimeter of the circular path; and 
 wherein both tissue engaging portions extend from the corresponding piercing distal tip thereof in a direction along the circular path that is the same as that in which the helical structure extends from the piercing distal tip thereof, either clockwise or counter-clockwise. 
 
     
     
       2. The electrode assembly of  claim 1 , wherein the fixed ends of the fixation members are located opposite one another, on either side of the helical structure. 
     
     
       3. The electrode assembly of  claim 2 , wherein the tissue engaging portion of each fixation member of the pair extends approximately one half of a turn along the circular path. 
     
     
       4. The electrode assembly of  claim 1 , wherein the tissue engaging portion of each fixation member of the pair extends between approximately one quarter of a turn and approximately one turn along the circular path. 
     
     
       5. The electrode assembly of  claim 1 , wherein the fixed end of each fixation member of the pair comprises a post that extends approximately parallel with the longitudinal axis, between the distal portion of the device and the tissue engaging portion of the corresponding fixation member. 
     
     
       6. The electrode assembly of  claim 5 , wherein the tissue engaging portion of each fixation member of the pair includes a first segment and a second segment, each first segment extending along the circular path and bending proximally from the corresponding post, toward the distal portion of the device, and each second segment extending along the circular path and distally from the corresponding first segment, away from the distal portion of the device. 
     
     
       7. The electrode assembly of  claim 5 , wherein the fixed end of each fixation member of the pair further comprises a base segment from which the corresponding post extends distally to the corresponding tissue engaging portion, the base segment of each fixation member extending along an arcuate path, around the longitudinal axis. 
     
     
       8. The electrode assembly of  claim 5 , wherein the post of at least one of the fixation members includes an extension that protrudes radially outward, away from the longitudinal axis. 
     
     
       9. The electrode assembly of  claim 1 , wherein the piercing distal tip of each fixation member is approximately coplanar with the piercing distal tip of the helical structure. 
     
     
       10. The electrode assembly of  claim 1 , wherein the piercing distal tip of each fixation member is proximally offset from the piercing distal tip of the helical structure. 
     
     
       11. The electrode assembly of  claim 1 , wherein the second electrode surface is formed on one or both of the fixation members. 
     
     
       12. The electrode assembly of  claim 1 , wherein an outer diameter of the helical structure is approximately 2 French, and an outer diameter defined by the tissue engaging portions of the fixation members is approximately 20 French.